Stock Level Import Script

A popular problem with Magento is how to import stock levels from another system, e.g. an ERP system. Although Magento has the API for easily carrying out such tasks it is s-l-o-w. Hence, here is an example of how to do it quickly and easily. This exceptionally well documented, clean code is thanks to michael_g08, see thread here: http://www.magentocommerce.com/boards/viewthread/32491